America's Most Challenging High Schools ranks schools through an index formula that's a simple ratio: the number of Advanced Placement, International Baccalaureate and Advanced International Certificate of Education tests given at a school each year, divided by the number of seniors who graduated that year. A ratio of 1.000 means the school had as many tests as graduates.

Uplift North Hills Preparatory in Texas is among the top five nationally. (Courtesy of Uplift Education)